Australian fire officials say the threat to the Blue Mountains west of Sydney "has been averted" for the day, but warn the crisis is far from over.

New South Wales Rural Fire Service Commissioner Shane Fitzsimmons said residents would be able to return to their homes.

But he warned that fresh challenges lay ahead in the coming days amid unfavourable conditions.

In total, 73 fires are burning across the state, 29 of which are uncontained.

Meanwhile, a fire service investigation has concluded the largest of the fires in the Blue Mountains - State Mine near Lithgow - was caused by explosives training at an army range at Marrangaroo last Wednesday.

'Fireballs fell around her'

Catherine Hubbard (pictured centre) was sleeping after a night shift as flames closed in on her home in Winmalee, 45 miles (70km) west of Sydney.

Her daughter Amy (also pictured) told the BBC of the frantic hours she and her brother had trying to contact Catherine by phone to warn her to leave.

The calls woke Catherine, who realised "there were fireballs falling all around her".

"She basically ran, grabbing the pets," said Amy.

They returned to the burnt-out remains of their home a few days ago. "We were crying. We are still in a lot of shock."

Mr Fitzsimmons confirmed the cause of the fire was "on a live firing range as a result of the detonation of some ordnance", but he said: "Any suggestion that this practice would be on par with someone deliberately lighting fires, reckless or criminal, is outrageous".

The defence department has not yet commented on the findings, but acknowledged at the weekend that it could have been the cause.

The findings have angered Blue Mountains Mayor Mark Greenhill who said the army "should not have been firing" on such a hot, dry day.

Hundreds of homes have already been destroyed as more than 3,000 firefighters battle to contain the bushfires in Australia's most populous state.

'Stay vigilant'

Fire officials had warned that Wednesday's combination of high temperatures, low humidity and strong winds could lead to more devastation.

But fire chiefs confirmed by the end of the day that not one home had been lost.

"If you have been someone that has chosen to depart the Blue Mountains today, to be out of harm's way, then it would be safe to head back home tonight because the risk has been averted," Mr Fitzsimmons said.

Media captionA drone captured the scene in the fire-hit city of Lithgow

Fire chiefs say a combination of back-burning - the controlled burning of areas with the aim of depriving a fire of fuel - building lines of containment and strategic planning had paid off.

In particular, firefighters on Tuesday merged the State Mine fire with one at Mount Victoria to prevent them linking up with the third. "It is absolutely wonderful it did not run," Mr Fitzsimmons said.

But he warned people to remain extremely vigilant.

"There are still fires flaring up," he said. "There's every prospect we're going to see some more."

Many schools in the Blue Mountains are expected to remain closed on Thursday. A major highway through the region is also closed.

Emergency alerts remain in place near the city of Newcastle, north of Sydney. An emergency alert in Springwood, to the west, has been downgraded to a watch-and-act alert.

How eucalyptus trees help bushfires to spread

Ninety percent of Australia's forests are eucalyptus trees that are adapted to bushfires. Eucalyptus leaves are rich in flammable oils and many varieties also have trunks that have evolved to burn quickly and later sprout new growth from buds in the bark (right)

The fastest-moving and most dangerous part of the fire is known as the "head". Areas ahead of the fire are warmed as it approaches and flying embers blown by the wind spark "spotfires", which cause it to leap further ahead

Earlier, new Prime Minister Tony Abbott hit back at comments by UN climate chief Christiana Figueres linking bushfires to global warming and criticising his decision to repeal a tax on carbon emissions introduced by the previous government.

"The official in question is talking through her hat," Mr Abbott told local media.

"Climate change is real, as I've often said, and we should take strong action against it. But these fires are certainly not a function of climate change - they're just a function of life in Australia."

Mr Abbott, who took office in September, has drafted legislation to repeal the carbon tax, which imposed a levy on the country's 300 biggest polluters.

The new prime minister, who says the tax cost jobs and forced energy prices up, wants to introduce a Direct Action plan under which farmers and industry will be paid to act to reduce emissions.